NEW YORK (CBSNewYork/AP) – New York City Mayor Michael Bloomberg says an investigation estimates that thousands of people with criminal records could have bought guns on just one classified ad website.

The group checked out 600 people who posted that they wanted to buy guns. It says one in 30 of them had a felony record, which excludes them from buying firearms. Bloomberg’s group extrapolated the data to conclude the site could have more than 25,000 illegal buyers a year.

“Convicted felons, domestic abusers and other dangerous people who are legally barred from buying guns can do so online, with little more than a phone number or email address,” Bloomberg said. “Not only are criminals buying guns online, they’re doing so brazenly by openly advertising that they want to buy them.”